1. Field of the Invention
The present invention relates to a printing process using a heat-sensitive lithographic printing plate and, more particularly, to a printing process using a lithographic printing plate, in which image recording can be conducted by scanning exposure based on a digital signal and image is formed in a lithographic printing original plate by processing with a simple printing machine, so that a printed matter can be stably obtained without using wetting water.
2. Description of the Related Art
In general, a lithographic printing plate is composed of an oleophilic image portion receiving an ink and a hydrophilic non-image portion receiving wetting water in the printing process. As the lithographic printing plate, a photosensitive (PS) plate composed of a hydrophilic support having thereon an oleophilic photosensitive resin layer has been widely used. In the prepress process using the same, generally, exposure is conducted through an original copy, such as a lith film, and a non-image portion is removed by dissolving with a developing solution, whereby a desired printing plate is obtained.
While such an operation is necessary after exposure that the non-image portion is removed by dissolving in the conventional prepress process using the PS plate, it is one of the problems of the conventional technique demanding to be solved that such an additional wet process is omitted (i.e., replaced by a dry process) or is simplified. Particularly, in recent years, since treatment of waste liquid discharged from the wet process has become a matter of concern to the industrial world, demand for improvement of the process in this respect is being increased.
As one simple prepress process addressing the demand, a process has been proposed that an image recording layer in which removal of a non-image portion of a printing plate original can be conducted through an ordinary printing process is used, and the layer is exposed and then developed on a printing machine, so as to obtain a final printing plate. The prepress process of the lithographic printing plate according to such a process is referred to as an on-machine developing process. Examples of the specific process include the use of an image recording layer that is soluble in wetting water or an ink solvent, and a process conducting mechanical removal by contact with an impression cylinder or a blanket cylinder. However, in the case where a conventional image recording material utilizing an ultraviolet ray or a visible ray is subjected to the on-machine development, because an image recording layer is not fixed even after exposure in such an image recording material, such a complicated operation becomes necessary that, for example, the original plate is stored under a completely light shielding condition or a completely-temperature constant condition until it is loaded on the printing machine.
As another trend in this field of art, a digitalization technique is being widely spread in which image information is electronically processed, accumulated and output provided by using a computer, and various novel image output processes are being subjected to practical use addressing the digitalization technique. According to the trend, a computer-to-plate technique receives an attention in which technique an original plate is exposed by scanning with a radiant ray of high astringency like laser beam carrying digitalized image information, so as to produce a printing plate in a direct manner without using a lith film. Accordingly, it becomes an important technical problem to obtain an original printing plate adapted to such a purpose.
Therefore, demands for simplification, use of a dry process and omission of the process for the prepress operation are being greatly increased from both the standpoints of environment and digitalization.
As a production process of a printing plate of scanning exposure type, which can be easily incorporated in the digitalization technique, a prepress process utilizing a solid laser of high output power, such as a semiconductor laser or a YAG laser, as an image recording means is receiving hopeful attention since the laser is available at low cost. In the conventional prepress process, image recording is conducted in such a manner that imagewise exposure of low or intermediate illuminance is applied to a photosensitive original plate to effect imagewise physical change on the surface of the original plate by a photochemical reaction. In a process using exposure of a high power density by a high output power laser, however, an exposed area is intensively irradiated with a large amount of light energy within a momentary exposure period, so as to effectively convert the light energy to heat energy, and thermal change, such as chemical change, phase change and change in shape and structure, is caused by the heat, so that the change is utilized for image recording. In other words, while the image information is input by light energy, such as laser light, the image recording is effected by a reaction caused by the heat energy. In general, such a recording mode utilizing the heat generation caused by the high power density exposure is referred to as heat mode recording, and the conversion of light energy to heat energy is referred to as photothermal conversion.
A remarkable advantage of the prepress process using the heat mode recording means is that exposure is not effected with an ordinary illuminance level, such as interior illumination, and a fixing operation is not necessary for an image recorded by the high illuminance exposure. In other words, when a heat mode sensitive material is utilized for image recording, it is not exposed by interior illumination, and an image does not have to be fixed after exposure. Therefore, for example, when a prepress process, in which an image recording layer which is made insolubilized or solubilized by the heat mode exposure is used and the exposed image recording layer is imagewise removed to form a printing plate, is conducted by the on-machine developing process, a printing system can be established in which the development (removal of the non-image portion) can be effected so that the image is not adversely affected even when the image is exposed to interior environmental illumination for a certain period after the imagewise exposure.
Therefore, it is expected that a lithographic printing plate original plate that is suitable for the on-machine developing process can be realized by utilizing the heat mode recording.
As one of preferred production processes for a lithographic printing plate based on the heat mode recording, such a process has been proposed that a hydrophobic image recording layer is provided on a hydrophilic substrate, which is subjected to imagewise heat mode exposure to change the solubility and the dispersibility of the hydrophobic layer, followed by removing, depending on necessity, the non-image portion by wet development.
Examples of the original plate of this type include a process for obtaining a printing plate in JP-B-46-27919, in which an original plate is subjected to heat mode recording, the original plate being composed of a hydrophilic support having thereon a recording layer exhibiting the so-called positive effect (where the solubility is increased by heat) a recording layer specifically having a particular composition containing a saccharide and a melamine formaldehyde resin.
However, since the recording layer thus disclosed has insufficient heat sensitivity, the sensitivity to the heat mode scanning exposure is insufficient. Furthermore, it is a practical problem that the discrimination between hydrophobicity and hydrophilicity before and after exposure, i.e., the change in solubility, is small. When the discrimination is poor, it is practically difficult to conduct prepress by the on-machine developing process.
WO98/40212 discloses a lithographic printing plate original that can be subjected to prepress without development, composed of a hydrophilic layer containing a transition metal oxide colloid formed on a substrate having an ink receiving layer containing a photothermal conversion agent coated thereon. In this original plate, the hydrophilic layer containing the transition metal oxide colloid is removed by ablation (scattering) by heat generated by the photothermal conversion agent at the exposed part. However, since the photothermal conversion agent is present on the side of the substrate, the heat converted from the absorbed light is dissipated toward the substrate, and thus the heat cannot be effectively utilized for the ablation of the hydrophilic layer, so as to cause a problem of low sensitivity. While JP-A-55-105560 and WO94/18005 disclose lithographic printing plate originals similar to the foregoing, each of which is composed of a hydrophilic layer that can be subjected to ablation provided on a substrate having a oleophilic photothermal conversion layer coated thereon, they have low sensitivity because of the similar reasons.
In order to avoid the drawback (i.e., the low density) of the heat-sensitive lithographic printing plate original which is subjected to ablation, WO99/19143 and WO99/19144 disclose lithographic printing plate originals having a hydrophilic layer containing colloid as an upper layer having a photothermal conversion agent added thereto. In this case, while the sensitivity is increased by the constitution, the addition of the photothermal conversion agent to the hydrophilic layer causes problems that the film quality of the hydrophilic layer is deteriorated to lower the printing durability, and in some cases, the hydrophilicity of the hydrophilic layer is impaired to contaminate a non-image portion with ink during printing.
Furthermore, in the conventional heat-sensitive lithographic printing plate original, because a laser exposure device and a light source are contaminated by the ablation (scattering) of the hydrophilic layer, a device for scavenging ablation dusts is necessary for these devices. However, it is difficult to sufficiently remove the contamination even though the scavenging device is provided.
Consequently, the prepress process and the printing process utilizing the heat mode image recording have an advantage that they can directly produce a press plate from an original copy without using a film, and thus the on-machine prepress can be conducted to omit the developing operation, but they also have the foregoing drawbacks.
On the other hand, as a simple process of lithographic printing using no wetting water, lithographic printing using an emulsion ink has been proposed in JP-B-49-26844, JP-B-49-27124, JP-B-49-27125, JP-A-53-36307, JP-A-53-36308, JP-B-61-52867, JP-A-58-2114844, JP-A-53-27803, JP-A-53-29807, JP-A-54-146110, JP-A-57-212274, JP-A-58-37069 and JP-A-54-106305. The emulsion ink is an emulsion of a water-containing ink, and since water and the ink is separated on the surface of a plate, it has such characteristics that water can be supplied from the ink, and therefore, no wetting water has to be supplied from the printing machine.
However, in the case where the emulsion ink is applied to the conventional lithographic printing plate having a non-image portion on the surface of an aluminum substrate having been made hydrophilic, there are problems in which water degradation is caused by excessive water, and background contamination is caused by shortage of water. As the quantitative balance between the ink and water supplied from the emulsion ink is constant, but the proportion of the non-image portion, to which water is supplied, and an image portion, to which the ink is supplied, greatly varies depending on printed matters to be produced, the latitude of a balance between the ink and water on the plate is small.
The present invention has been developed to solve the foregoing problem associated with the conventional heat mode prepress process using laser exposure and the foregoing problem associated with the case where an emulsion ink is applied.
That is, a first object of the invention is to provide a lithographic printing process in which printing is conducted without using wetting water by using a heat-sensitive lithographic printing plate original that can be subjected to prepress by a simple on-machine process, so as to provide stable printed matter without contamination on a non-image portion or dropout on an image portion.
A second object of the present invention is to provide a lithographic printing process conducting printing without the use of wetting water by applying an emulsion ink, in which a printed matter of stable high quality can be easily obtained irrespective of the balance between an image portion and a non-image portion.
A third object of the invention is to provide a lithographic printing process using an emulsion ink, in which a novel hydrophilic layer that can suitably address supply of water from an emulsion ink is utilized as a non-image portion.
As a result of extensive investigations made by the inventors, it has been found that scattering of ablation dusts of a heat-sensitive layer and a hydrophilic layer can be prevented without deterioration in printing suitability and sensitivity by providing an overcoat layer, and the removal of the overcoat layer and the hydrophilic layer on the printing plate can be effectively conducted by using an emulsion ink as the ink, so as to accomplish the first object of the invention.
That is, in a first characteristic feature of the lithographic printing process according to the invention, image recording is conducted on a heat-sensitive lithographic printing plate original having an overcoat layer that can be removed upon printing, and then printing is conducted by using an emulsion ink.
In a preferred embodiment of the invention, the heat-sensitive lithographic printing plate original comprises a heat-sensitive layer having an ink receiving surface, a hydrophilic layer and the overcoat layer provided on the heat-sensitive layer in this order, and in the process for forming an image, the adhesiveness between the heat-sensitive layer and the hydrophilic layer is decreased in the heated region by a thermal action applied on a surface of the heat-sensitive layer to enable removal of the hydrophilic layer, so as to effect image recording, and thereafter, in the process for printing, the emulsion ink is supplied to the plate surface, so as to remove the overcoat layer and the heated region of the hydrophilic layer by a hydrophilic component of the ink.
It is preferred at this time that the overcoat layer contains a photothermal conversion agent, which converts laser light to heat, from the standpoint of improvement in sensitivity and image formation property.
According to the first characteristic feature of the invention, since an overcoat layer that can be removed upon printing, i.e., is hydrophilic, is the uppermost layer of the lithographic printing plate original, scattering due to ablation of a heat-sensitive layer and a hydrophilic layer caused by exposure or heating can be prevented, and furthermore, the hydrophilic overcoat layer is easily removed by conducting printing using an emulsion ink containing a hydrophilic component, whereby the printing suitability, such as printing durability and contamination resistance, and the sensitivity are not impaired.
In the printing process according to the invention, heating on forming an image is preferably effected by exposure with laser light, such as an infrared laser.
In the case where the overcoat layer is transparent to the exposure wavelength for image formation, the layer does not influence the sensitivity, and in the case the layer contains a photothermal conversion agent having absorbance at the exposure wavelength, it contributes to improving the sensitivity.
As a result of extensive investigations made by the inventors, it has been found that a lithographic printing plate having, on a non-image portion, a hydrophilic layer having an inorganic matrix formed by sol-gel conversion can be used, so as to solve the foregoing problems, whereby the second and third objects of the invention have been accomplished.
That is, in the second characteristic feature of the invention, image recording is effected on a lithographic printing plate original to form a non-image portion formed with a hydrophilic layer having an inorganic matrix formed by sol-gel conversion, and thereafter, printing is conducted by using an emulsion ink which is obtained by adding a hydrophilic component mainly comprising water and/or a polyhydric alcohol to an oleophilic ink component and emulsifying the mixture.
In this characteristic feature of the invention, the lithographic printing plate original used for the lithographic printing process preferably comprises a support having thereon a hydrophilic layer having an inorganic matrix formed by sol-gel conversion.
According to this characteristic feature of the invention, a non-image portion is formed with the hydrophilic layer having the inorganic matrix formed by sol-gel conversion that has a function suitable for conducting printing by using an emulsion ink, whereby printed matter of high quality can be stably provided.
It is not completely clear why the hydrophilic layer having the inorganic matrix formed by sol-gel conversion effectively functions in printing using an emulsion ink. It is considered as one factor that since the hydrophilic layer having the inorganic matrix formed by sol-gel conversion is hydrophilic and simultaneously has some organic groups in comparison to the conventional aluminum substrate surface, it has higher affinity to the polyhydric alcohol component contained in the hydrophilic component in the emulsion ink, and thus sufficient ink repellance can be obtained even in the case where the amount of the hydrophilic component present on the plate surface is small. It is also considered as another factor that since the hydrophilic layer having the inorganic matrix formed by sol-gel conversion is a porous film, the hydrophilic components in the emulsion ink can be effectively retained inside the layer even when the amount of the hydrophilic component present on the plate surface is excessive, whereby the latitude of the balance between the amount of an oleophilic ink component and a hydrophilic component on the plate surface is large.
A first embodiment of the invention will be described in more detail below.
The heat-sensitive lithographic printing plate original applied in the printing process of this embodiment has such a characteristic feature that it comprises an overcoat layer that can be removed in printing, and the overcoat layer is easily removed by an emulsion ink used in printing.
The emulsion ink used in this embodiment is an emulsion ink formed by adding and emulsifying a hydrophilic component in an oleophilic ink component, and may be either a W/O (water in oil) type or an O/W (oil in water) type. The emulsion ink used in this embodiment maintains a stable emulsion state under the storage condition in an ink canister and in an ink container upon application to printing, and when the ink is transferred through an inking system (ink supplying system) upon printing under application of a shearing force to reach an ink supplying roller, the emulsion state is broken to separate the hydrophilic component to be supplied to the plate surface. On the plate surface, the hydrophilic component is attached to the non-image region to form a liquid film to prevent attachment of the oleophilic ink component, and the oleophilic ink component is attached to the image portion. The emulsion ink can be used in this embodiment without particular limitation, as long as it has the foregoing function.
In order to exhibit the foregoing function by the emulsion ink used in this embodiment, it is preferred to use a printing machine having an inking system equipped with a cooling mechanism.
The ratio of the oleophilic ink component and the hydrophilic component in the emulsion ink of this embodiment is that the amount of the hydrophilic component is from 5 to 150 parts by weight, and preferably from 20 to 100 parts by weight, per 100 parts by weight of the oleophilic ink component.
As the oleophilic ink component of the emulsion ink of this embodiment, an ordinary oleophilic ink can be used, which includes, for example, a vegetable oil, a synthetic resin varnish, a natural resin varnish, a synthetic varnish thereof, a high boiling point petroleum solvent, a pigment and other additives (such as an abrasion resistance improving agent, an ink dryer and a drying suppressing agent).
As the hydrophilic component of the emulsion ink of this embodiment, water and/or a polyhydric alcohol can be used.
Examples of the polyhydric alcohol include glycerin, diglycerin, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, hexylene glycol, sorbitol, butanediol and pentanediol. Among these, glycerin, ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol are preferably used.
The polyhydric alcohol may be used singly or in a combination of two or more, and may be used as a mixture with water.
In the hydrophilic component in this embodiment, the content of the polyhydric alcohol is preferably from 30 to 100% by weight, and more preferably from 50 to 100% by weight.
In the hydrophilic component of the emulsion ink in this embodiment, an additive may be used in addition to the foregoing for improvement of emulsion stability, improvement of flow characteristics, improvement of hydrophilicity and suppression of evaporation of the hydrophilic component.
Examples of the additive include a monovalent alcohol, such as methanol and ethanol, an aminoalcohol, such as monoethanolamine and diethanolamine, a known surface active agent, such as a nonionic series, an anionic series, a cationic series and a betaine series, an oxycarboxylic acid, such as glycolic acid, lactic acid and citric acid, a hydrophilic polymer, such as polyvinylpyrrolidone, polyacrylic acid, gum arabic and carboxymethyl cellulose, and an inorganic or organic salt, such as a phosphate, silicate, nitrate and a salt thereof.
Examples of the thermal action for conducting image recording include direct thermal energy itself by, for example, a thermal recording head, and those by thermal energy obtained by converting light, such as an infrared laser, to heat with a photothermal conversion agent.
A heat sensitive lithographic printing plate original that can be used in this embodiment is a heat-sensitive lithographic printing plate having an overcoat layer as the uppermost layer that can be removed upon printing and can be subjected to image recording with a thermal action. The fact that it can be subjected to image recording with a thermal action herein means that it has a heat-sensitive layer that can be chemically and/or physically changed by the action of heat, and it involves, for example, a heat-sensitive lithographic printing plate original having such a heat-sensitive layer that enables image recording by utilizing decrease or increase of an interface adhesion property to the adjacent layer by thermal fusion, thermal decomposition or thermal crosslinking of the heat-sensitive layer, decrease or increase of the solubility of the heat-sensitive layer itself, or polarity change or phase change of the heat-sensitive layer.
Among these, a lithographic printing plate original that enables image recording by decrease of the interface adhesion property to the layer adjacent to the heat-sensitive layer by chemical and/or physical change can be preferably used.
Specific examples thereof include an embodiment of a heat-sensitive lithographic printing plate original comprising a heat-sensitive layer having an ink receiving surface having thereon a hydrophilic layer and an overcoat layer in this order. In this embodiment, the surface of the heat-sensitive layer receives the thermal function at a heated part to decrease the adhesion to the hydrophilic layer, whereby removal of the hydrophilic layer at that part becomes possible. Therefore, in the case where this embodiment of the heat-sensitive lithographic printing plate original is applied to printing by using the emulsion ink after image recording, the hydrophilic layer at the heated part can be easily removed along with the overcoat layer on the printing machine, so as to enable printing.
While an embodiment of a heat-sensitive lithographic printing plate original comprising a heat-sensitive layer having an ink receiving surface having thereon a hydrophilic layer and an overcoat layer in this order will be described in more detail below, the present invention is not construed as being limited to this embodiment.
The overcoat layer used in this embodiment is a layer that is easily removed by supplying an emulsion ink to the plate surface upon printing, and that has a function of protecting the hydrophilicity of the surface of the hydrophilic layer, and it preferably contains a polymer compound capable of forming a film. The function that it is removed with the emulsion ink includes a case of forming a hydrophilic film that is removed by the hydrophilic component contained in the ink and a case of forming an oleophilic film that is removed by the ink component, and it is preferred to form the hydrophilic film from the standpoint of easiness of removal as described in detail below.
The overcoat layer of this embodiment can be provided in the following manner. A coating solution containing the polymer compound can be coated and dried directly on the hydrophilic layer, or in alternative, the coating solution is coated and dried on a separate support, and then it is provided on the hydrophilic layer by lamination, followed by releasing and removing the support.
The polymer used in the overcoat layer of this embodiment may be a known organic or inorganic resin. It is preferably one having a film forming function capable of forming a film, and in order for easy removal upon printing with the emulsion ink, it is preferably easily dissolved or dispersed in the hydrophilic component of the emulsion ink, particularly water and/or a polyhydric alcohol. A hydrophilic polymer is preferred as the polymer, and specific examples thereof include polyvinyl acetate (provided that it has a hydrolysis degree of 65% or more), polyacrylic acid and an alkali metal salt or an amine salt thereof, a polyacrylic acid copolymer and an alkali metal salt or an amine salt thereof, polymethacrylic acid and an alkali metal salt or an amine salt thereof, a polymethacrylic acid copolymer and an alkali metal salt or an amine salt thereof, polyacrylamide and a copolymer thereof, polyhydroxyethylene acrylate, polyvinyl pyrrolidone and a copolymer thereof, polyvinyl methyl ether, a polyvinyl methyl ether-maleic anhydride copolymer, poly-2-acrylamide-2-methyl-1-propanesulfonic acid and an alkali metal salt or an amine salt thereof, a poly-2-acrylamide-2-methyl-1-propanesulfonic acid copolymer and an alkali metal salt or an amine salt thereof, gum arabic, a cellulose derivative (such as carboxymethyl cellulose, carboxyethyl cellulose and methyl cellulose) and a modified product thereof, white dextrin, pullulan and enzyme decomposition etherified dextrin. These resins may be used by mixing two or more thereof depending on purpose.
In the case where image recording of the heat-sensitive lithographic printing plate original in this embodiment is conducted by using laser light, the overcoat layer preferably has a photothermal conversion function and preferably contains a photothermal conversion substance in addition to the foregoing polymer from the standpoint of improvement of the sensitivity. The photothermal conversion substance used in the overcoat layer in this embodiment is not particularly limited as long as it has such a function that it absorbs light having the wavelength used for exposure, i.e., light having a wavelength of 700 nm or more in the case of an infrared laser, to generate heat, and various known pigments and dyes can be used. In order for easy removal thereof upon printing with the emulsion ink as similar to the polymer, it is preferred that the substance is easily dissolved or dispersed in the hydrophilic component of the emulsion ink, particularly water and/or a polyhydric alcohol.
As the pigment, commercially available pigments and the pigments disclosed in the Color Index (C.I.) Reference, xe2x80x9cSaishin Ganryo Binran (Newest Pigment Handbook)xe2x80x9d (edited by Society of Pigment Engineering Japan, 1977), xe2x80x9cSaishin Ganryo Oyo Gijutu (Newest Pigment Application Technique)xe2x80x9d (published by CMC Publications, 1986), xe2x80x9cInsatu Ink Gijutu (Printing Ink Technique)xe2x80x9d (published by CMC Publications, 1984) can be used.
Examples of species of the pigment include a black pigment, a brown pigment, a red pigment, a violet pigment, a blue pigment, a green pigment, a fluorescent pigment, a metallic powder pigment and a polymer binding pigment. Specific examples thereof include an insoluble azo pigment, an azo lake pigment, a condensation azo pigment, a chelate azo pigment, a phthalocyanine series pigment, an anthraquinone series pigment, a perylene and perynone series pigment, a thioindigo series pigment, a quinacridone series pigment, a dioxane series pigment, an isoindolinone series pigment, a quinophthalone series pigment, a dyeing lake pigment, an azine pigment, a nitroso pigment, a nitro pigment, a natural pigment, a fluorescent pigment, an inorganic pigment and carbon black.
The pigments may be used without conducting a surface treatment or may be used after conducting a surface treatment. It is considered that examples of the method for conducting surface treatment include a method of surface coating a hydrophilic resin or an oleophilic resin, a method of attaching a surface active agent, a method of bonding a reactive substance (such as silica gel, alumina sol, a silane coupling agent, an epoxy compound and an isocyanate compound) on the surface of the pigment. The methods for the surface treatment are disclosed in xe2x80x9cKinzoku Sekken no Seisitsu to Oyo (Nature and Application of Metallic Soap)xe2x80x9d (published by Saiwai Shobo), xe2x80x9cInsatsu Ink Gijutu (Printing Ink Technique)xe2x80x9d (published by CMC Publishing, 1984) and xe2x80x9cSaishin Ganryo Oyo Gijutu (Newest Pigment Application Technique)xe2x80x9d (published by CMC Publications, 1986). Among the pigments, those absorbing infrared light or near infrared light are preferred from the standpoint that they are suitable for the use of a laser emitting infrared light or near infrared light.
Preferred examples of the pigment that absorbs infrared light or near infrared light include carbon black, carbon black coated with a hydrophilic resin and carbon black modified with silica sol. Among these, carbon black having a surface coated with a hydrophilic resin or silica sol is useful since it is easily dispersed with a water soluble resin and does not impair the hydrophilicity.
The particle diameter of the pigment is preferably in the range of from 0.01 to 1 xcexcm, and more preferably in the range of from 0.01 to 0.5 xcexcm. A known dispersion technique used for production of an ink and production of a toner can be used as a method of dispersing the pigment. Examples of the disperser include an ultrasonic disperser, a sand mill, an Attritor, a Perl mill, a super mill, a ball mill, an impeller, a Disperser, a KD mill, a colloid mill, a Dynatron, a three-roll mill and a pressure kneader. These dispersers are described in detail in xe2x80x9cSaishin Ganryo Oyo Gijutu (Newest Pigment Application Technique)xe2x80x9d (published by CMC Publications, 1986).
As the dye, commercially available dyes and those disclosed in the literatures (such as xe2x80x9cSenryo Binran (Dye Handbook)xe2x80x9d edited by Association of Organic Synthetic Chemistry, 1970) can be used. Specific examples thereof include an azo dye, a metallic complex salt azo dye, a pyrazolone azo dye, an anthraquinone dye, a phthalocyanine dye, a carbonium dye, a quinoneimine dye, a methine dye and a cyanine dye. Among the dyes, those absorbing infrared light or near infrared light are preferred from the standpoint that they are suitable for the use of a laser emitting infrared light or near infrared light.
Examples of the dye absorbing infrared light or near infrared light include cyanine dyes disclosed in JP-A-58-125246, JP-A-59-84356, JP-A-59-202829 and JP-A-60-78787, methine dyes disclosed in JP-A-58-173696, JP-A-58-181690 and JP-A-58-194595, naphthoquinone dyes disclosed in JP-A-58-112793, JP-A-58-224793, JP-A-59-48187, JP-A-59-73996, JP-A-60-52940 and JP-A-60-63744, a squarylium dye disclosed in JP-A-58-112792, a cyanine dye disclosed in British Patent No. 434,875, and the dyes disclosed as formulae (I) and (II) below in U.S. Pat. No. 4,756,993: 
wherein R1, R2, R3, R4, R5 and R6 each represents a substituted or unsubstituted alkyl group; Z1 and Z2 each represents a substituted or unsubstituted phenyl group or a substituted or unsubstituted naphthalene group; L represents a substituted or unsubstituted methine group, wherein when the methine group has a substituent, the substituent may be an alkyl group having 8 or less carbon atoms, a halogen atom or an amino group, or in alternative the methine group may include a cyclohexane ring or a cyclopentane group which may have a substituent group formed by combining substituents on the two methine carbon atoms of the methine group, and the substituent group may be an alkyl group having 6 or less carbon atoms or a halogen atom; X represents an anionic group; and n represents an integer of 1 or 2, provided that at least one of R1, R2, R3, R4, R5, R6, Z1 and Z2 represents an alkali metallic salt group or an amine salt group of an acidic group or a basic group, 
wherein R11 represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group; R12 and R15 each represents a hydrogen atom or a group that can be substituted instead of a hydrogen atom; R13 and R14 each represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkoxy group or a substituted or unsubstituted alkyl group, provided that both R13 and R14 do not simultaneously represent hydrogen atoms; and R16 and R17 each represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group; an acyl group or a sulfonyl group, provided that R16 and R17 may be combined to form a 5-membered or 6-membered ring.
The infrared absorption sensitizing agent disclosed in U.S. Pat. No. 5,156,938 is preferably used as the dye, and a substituted arylbenzo(thio)pyrylium salt disclosed in U.S. Pat. No. 3,881,924, a trimethinethiapyrylium salt disclosed in JP-A-57-142645 (corresponding to U.S. Pat. No. 4,327,169), pyrylium series compounds disclosed in JP-A-58-181051, JP-A-58-220143, JP-A-59-41363, JP-A-59-84248, JP-A-59-84249, JP-A-59-146063 and JP-A-59-146061, a cyanine dye disclosed in JP-A-59-216146, a pentamethinethiopyrylium salt disclosed in U.S. Pat. No. 4,283,475, a pyrylium compound disclosed in JP-B-5-13514 and JP-B-5-19702, and EPOLIGHT III-178, EPOLIGHT III-130 and EPOLIGHT III-125 produced by Epolin, Inc. are particularly preferably used. Among these dyes, the water soluble cyanine dye represented by the general formula (I) is especially preferred.
Specific examples of the compound, Example Compounds (I-1) to (I-32), will be listed below, but the present invention is not construed as being limited thereto.

The amount of the pigment or the dye is from 1 to 70% by weight, and preferably from 2 to 50% by weight, based on the total solid content of the overcoat layer. In the case of the dye, the amount is particularly preferably from 2 to 30% by weight, and in the case of the pigment, it is particularly preferably from 20 to 50% by weight. If the addition amount of the pigment or the dye is less than the range, the sensitivity is lowered, and if it exceeds the range, the uniformity of the layer is lost, to deteriorate the durability of the layer.
In the overcoat layer, a plasticizer, a pigment, a dye, a surface active agent, particles and an adhesion improving agent, for example, maybe added for improvement of the physical strength of the film, improvement of the dispersibility of the compositions constituting the film, improvement of the coating property, improvement of the removing property of the film and improvement of adhesion property to the surface of the heat-sensitive lithographic printing plate original.
For example, in the case where the overcoat layer is provided by coating an aqueous solution, a nonionic surface active agent is mainly added to improve uniformity of coating. Specific examples of the nonionic surface active agent include sorbitan tristearate, sorbitan monopalmitate, sorbitan trioleate, stearic monoglyceride and polyoxyethylene nonyl phenyl ether.
The amount of the nonionic surface active agent is preferably from 0.05 to 5% by weight, and more preferably from 1 to 3% by weight, based on the total solid content of the overcoat layer.
If thickness of the overcoat layer used in this embodiment is preferably from 0.05 to 4.0 xcexcm, and more preferably from 0.1 to 1.0 xcexcm.
If the overcoat layer is too thick, the period of time required for removing on the machine upon printing is prolonged, and there is a possibility that a large amount of the component of the overcoat layer dissolved exhibits adverse affect. If it is too thin, there are cases where the film property is impaired. In the case where the overcoat layer contains the photothermal conversion substance, there is a tendency that the heating efficiency of the lithographic printing plate original is lowered if it is too thick or too thin depending on the content of the substance.
The hydrophilic layer that can be used in this embodiment is such a layer that adhesion to the heat-sensitive layer is lowered corresponding to chemical and/or physical change of the lower layer due to heat from the surface of the heat-sensitive layer, and also such a layer that receives and retains the hydrophilic component of the emulsion ink upon printing, so as to function as the non-image portion.
Preferred examples of the hydrophilic layer of this embodiment include an organic hydrophilic matrix obtained by crosslinking or quasi-crosslinking an organic hydrophilic polymer, an inorganic hydrophilic matrix obtained by sol-gel conversion by hydrolysis and a condensation reaction of polyalkoxysilane, titanate, zirconate or aluminate, and a thin film of a metal or a metallic compound having a hydrophilic surface.
Examples of the crosslinking reaction used for forming the organic hydrophilic matrix of the hydrophilic layer of this embodiment include formation of a covalent bond by heat or light and formation of an ionic bond by a polyvalent metallic salt.
As the organic hydrophilic polymer used in this embodiment, a polymer having a functional group that can be used for the crosslinking reaction is preferred.
Preferred examples of the functional group include xe2x80x94OH, xe2x80x94SH, xe2x80x94NH2, xe2x80x94NHxe2x80x94, xe2x80x94COxe2x80x94NH2xe2x80x94, xe2x80x94COxe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94NHxe2x80x94, xe2x80x94NHxe2x80x94COxe2x80x94NHxe2x80x94, xe2x80x94COxe2x80x94OH, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94CSxe2x80x94OH, xe2x80x94COxe2x80x94SH, xe2x80x94CSxe2x80x94SH, xe2x80x94SO3H, xe2x80x94SO2(Oxe2x88x92), xe2x80x94PO3H2, xe2x80x94PO(Oxe2x88x92)2, xe2x80x94SO2xe2x80x94NH2, xe2x80x94SO2xe2x80x94NHxe2x80x94, xe2x80x94CHxe2x95x90CH2, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94COxe2x80x94C(CH3)xe2x95x90CH2, xe2x80x94COxe2x80x94CHxe2x95x90CH2, xe2x80x94COxe2x80x94CH2xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94CHxe2x80x94CH2, and the functional groups having the following structures, and among these, a hydroxyl group, an amino group, a carboxyl group and an epoxy group are preferred. 
As the organic hydrophilic polymer of this embodiment, a known water soluble binder can be used, and examples there of include polyvinyl alcohol (polyvinyl acetate having a saponification degree of 60% or more), modified polyvinyl alcohol, such as carboxyl-modified polyvinyl alcohol, starch and a derivative thereof, a cellulose derivative, such as carboxymethyl cellulose, a salt thereof and hydroxyethyl cellulose, casein, gelatin, gumarabic, polyvinyl pyrrolidone, polyvinyl sulfonic acid and a salt thereof, polyhydroxyethyl methacrylate, polyhydroxymethyl acrylate, polyacrylamide, a vinyl acetate-crotonic acid copolymer and a salt thereof, a styrene-maleic acid copolymer and a salt thereof, polyacrylic acid and a salt thereof, polymethacrylic acid and a salt thereof, polyethylene glycol, polyethyleneimine, polyvinyl sulfonic acid and a salt thereof, polystyrene sulfonic acid and a salt thereof, poly(methacryloyloxypropanesulfonic acid) and a salt thereof, polyvinyl sulfonic acid and a salt thereof, poly(methacryloyloxyethyltrimethylammoniumchloride), polyhydroxyethyl methacrylate, polyhydroxyethyl acrylate and polyacrylamide.
These polymers may be a copolymer as long as the hydrophilicity thereof is not impaired, and may be used singly or in a combination of two or more. The amount used thereof is from 20 to 99% by weight, preferably from 25 to 95% by weight, and more preferably from 30 to 90% by weight, based on the total solid content of the hydrophilic layer.
In this embodiment, crosslinking of the organic hydrophilic polymer can be conducted with a crosslinking agent. Examples of known crosslinking agents include a polyfunctional isocyanate compound, a polyfunctional epoxy compound, a polyfunctional amine compound, a polyol compound, a polyfunctional carboxyl compound, an aldehyde compound, a polyfunctional (meth) acrylic compound, a polyfunctional vinyl compound, a polyfunctional mercapto compound, a polyvalent metallic salt compound, a polyalkoxysilane and a hydrolyzed product thereof, a polyalkoxytitanium compound and a hydrolyzed product thereof, a polyalkoxyaluminum compound and a hydrolyzed product thereof, a polymethylol compound and a polyalkoxymethyl compound, and a known reaction catalyst may be added to accelerate the reaction.
The use amount thereof is from 1 to 50% by weight, preferably from 3 to 40% by weight, and more preferably from 5 to 35% by weight, based on the total solid content of the coating solution for the hydrophilic layer.
A system capable of conducting the sol-gel conversion that can be used for forming the inorganic matrix of the hydrophilic layer of this embodiment is such a polymeric body that bonding groups derived from a polyvalent element form a network structure through oxygen atoms, a polyvalent metal simultaneously has a non-bonded hydroxyl group and an alkoxy group, and all of which are present as resin structures in the mixed manner, which the polymeric body is in a sol state in the stage where the amount of the alkoxy group and the hydroxyl group is large, and the network resin structure becomes firm with the progress of formation of ether bonds. The system also has such a function that a part of the hydroxyl groups is bonded to solid fine particles to modify the solid fine particles, whereby the hydrophilicity is changed. Examples of the polyvalent bonding element having the hydroxyl group and the alkoxy group conducting the sol-gel conversion include aluminum, silicon, titanium and zirconium, any of which may be used in this embodiment. A sol-gel conversion system using a siloxane bond, which is most preferably used therein, will be described below. The sol-gel conversion using aluminum, titanium or zirconium can be effected by replacing the silicon in the following description by the respective elements.
That is, what is particularly preferably used is a system containing a silane compound having at least one silanol group that can effect the sol-gel conversion.
The system using the sol-gel conversion will be described in more detail below. The inorganic hydrophilic matrix formed by the sol-gel conversion is preferably a resin having a siloxane bond and a silanol group, which is formed in such a manner that, when a coating liquid, which is a sol system containing a silane compound having at least one silanol group, is coated, dried and aged, hydrolytic condensation of the silanol group proceeds to form a structure of a siloxane skeleton to advance gelation.
The foregoing organic hydrophilic polymer and the crosslinking agent may be added to the matrix having the gel structure for improvement of the physical properties, such as the film strength and the flexibility, improvement of the coating property and adjustment of the hydrophilicity.
The siloxane resin having the gel structure is represented by the following general formula (I), and the silane compound having at least one silanol group can be obtained by hydrolysis of a silane compound represented by the following general formula (II). The silane compound is not necessarily a partial hydrolysis product of the silane compound of the general formula (II) solely, and in general, the silane compound is formed with an oligomer formed by partial hydrolytic polymerization of the silane compound, or in alternative, a mixed composition of the silane compound and the oligomer. 
The siloxane-based resin of the general formula (I) is formed by the sol-gel conversion of at least one compound of the silane compound of the general formula (II), and at least one of R01 to R03 in the general formula (I) represents a hydroxyl group, and the others each represents the organic residual groups for R0 and Y in the general formula (II).
(R0)nSi(Y)4xe2x88x92nxe2x80x83xe2x80x83General Formula (II)
In the general formula (II), R0 represents a hydroxyl group, a hydrocarbon group or a heterocyclic group; Y represents a hydrogen atom, a halogen atom (which represents a fluorine atom, a chlorine atom, a bromine atom or an iodine atom), xe2x80x94OR1, xe2x80x94OCOR2 or xe2x80x94N(R3)(R4) (in which R1 and R2 each represents a hydrocarbon group, and R3 and R4 each independently represents a hydrogen atom or a hydrocarbon group); and n represents 0, 1, 2 or 3.
Examples of the hydrocarbon group or the heterocyclic group represented by R0 in the general formula (II) include:
(a) a substituted or unsubstituted linear or branched alkyl group having from 1 to 12 carbon atoms (such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group and a dodecyl group, examples of a group substituted on these groups include a halogen atom (such as a chlorine atom, a fluorine atom and a bromine atom), a hydroxyl group, a thiol group, a carboxyl group, a sulfo group, a cyano group, an epoxy group, an xe2x80x94ORxe2x80x2 group (wherein Rxe2x80x2 represents an methyl group, an ethyl group, a propyl group, a butyl group, a heptyl group, a hexyl group, an octyl group, a decyl group, a propenyl group, a butenyl group, a hexenyl group, a octenyl group, a 2-hydroxyethyl group, a 3-chloropropyl group, a 2-cyanoethyl group, N,N-dimethylaminoethyl group, a 1-bromoethyl group, a 2-(2-methoxyethyl)oxyethyl group, a 2-methoxycarbonylethyl group, a 3-carboxypropyl group or a benzyl group), an xe2x80x94OCORxe2x80x3 group (wherein Rxe2x80x3 represents the same contents as Rxe2x80x2), a xe2x80x94COORxe2x80x3 group, a xe2x80x94CORxe2x80x3 group, an xe2x80x94N(Rxe2x80x2xe2x80x3)(Rxe2x80x2xe2x80x3) group (wherein Rxe2x80x2xe2x80x3 represents the same contents as Rxe2x80x2 and the plurality thereof may be the same as each other or different from each other), an xe2x80x94NHCONHRxe2x80x3 group, an xe2x80x94NHCOORxe2x80x3 group, an xe2x80x94Si(Rxe2x80x3)3 group, a xe2x80x94CONHRxe2x80x2xe2x80x3 group and an xe2x80x94NHCORxe2x80x3 group, and the plurality of the substituents may be substituted in the alkyl group);
(b) a substituted or unsubstituted linear or branched alkenyl group having from 2 to 12 carbon atoms (such as a vinyl group, a propenyl group, a butenyl group, a pentenyl group, a hexenyl group, an octenyl group, a decenyl group and a dodecenyl group, examples of a group substituted on these groups include the same contents as described for the group substituted on the alkyl group, and the plurality of the substituents may be substituted in the alkyl group);
(c) a substituted or unsubstituted aralkyl group having from 7 to 14 carbon atoms (such as a benzyl group, a phenethyl group, a 3-phenylpropyl group, a naphthylmethyl group and a 2-naphthylethyl group, examples of a group substituted on these groups include the same contents as described for the group substituted on the alkyl group, and the plurality of the substituents may be substituted in the alkyl group);
(d) a substituted or unsubstituted alicyclic group having from 5 to 10 carbon atoms (such as a cyclopentyl group, a cyclohexyl group, a 2-cyclohexylethyl group, a 2-cyclopentylethyl group, a norbornyl group and an adamantane group, examples of a group substituted on these groups include the same contents as described for the group substituted on the alkyl group, and the plurality of the substituents may be substituted in the alkyl group);
(e) a substituted or unsubstituted aryl group having from 6 to 12 carbon atoms (such as a phenyl group and a naphthyl group, examples of a group substituted on these groups include the same contents as described for the group substituted on the alkyl group, and the plurality of the substituents may be substituted in the alkyl group); and
(f) a heterocyclic group containing at least one kind of atom selected from a nitrogen atom, an oxygen atom and a sulfur atom, which may be condensed (such as a pyran ring, a furan ring, a thiophene ring, a morpholine ring, a pyrrole ring, a thiazole ring, an oxazole ring, a pyridine ring, a piperidine ring, a pyrrolidone ring, a benzothiazole ring, a benzoxazole ring, a quinoline ring and a tetrahydrofuran ring, which may have a substituent, examples of a group substituted on these groups include the same contents as described for the group substituted on the alkyl group, and the plurality of the substituents may be substituted in the alkyl group).
Examples of the substituent on the groups xe2x80x94OR1, xe2x80x94OCOR2 and xe2x80x94N(R3)(R4) represented by Y in the general formula (II) include the following.
In the group xe2x80x94OR1, R1 represents a substituted or unsubstituted aliphatic group having from 1 to 10 carbon atoms (such as a methyl group, an ethyl group, a propyl group, a butyl group, a heptyl group, a hexyl group, a pentyl group, an octyl group, a nonyl group, a decyl group, a propenyl group, a butenyl group, a heptenyl group, a hexenyl group, an octenyl group, a decenyl group, a 2-hydroxyethyl group, a 2-hydroxypropyl group, a 2-methoxyethyl group, a 2-(methoxyethyloxo)ethyl group, a 1-(N,N-diethylamino)ethyl group, a 2-methoxypropyl group, a 2-cyanoethyl group, a 3-methyloxapropyl group, a 2-chloroethyl group, a cyclohexyl group, a cyclopentyl group, a cyclooctyl group, a chlorocyclohexyl group, a methoxycyclohexyl group, a benzyl group, a phenethyl group, a dimethoxybenzyl group, a methylbenzyl group and a bromobenzyl group).
In the group xe2x80x94OCOR2, R2 represents the same aliphatic group as in R1 or a substituted or unsubstituted aromatic group having from 6 to 12 carbon atoms (examples of the aromatic group include those exemplified for the aryl group represented by R).
In the group xe2x80x94N(R3)(R4), R3 and R4, which may be the same or different, each represents a hydrogen atom or a substituted or unsubstituted aliphatic group having from 1 to 10 carbon atoms (such as those exemplified for R1 in the group xe2x80x94OR1).
Examples of the silane compound represented by the general formula (II) will be listed below, but the invention is not limited thereto.
Examples thereof include tetrachlorosilane, tetrabromosilane, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetra-n-propylsilane, tetra-t-butoxysilane, tetra-n-butoxysilane, dimethoxyethoxy silane, methyltrichlorosilane, methyltribromosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltri-t-butoxysilane, ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, ethyltri-t-butoxysilane, n-propyltrichlorosilane, n-propyltribromosilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltriisopropoxy silane, n-propyltri-t-butoxysilane, n-hexyltrichlorosilane, n-hexyltribromosilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-hexyltriisopropoxysilane, n-hexyltri-t-butoxysilane, n-decyltrichlorosilane, n-decyltriboromosilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, n-decyltriisopropoxysilane, n-decyltri-t-butoxysilane, n-octadecyltrichlorosilane, n-octadecyltribromosilane, n-octadecyltrimethoxysilane, n-octadecyltriethoxysilane, n-octadecyltriisopropoxysilane, n-octadecyltri-t-butoxysilane, phenyltrichlorosilane, phenyltribromosilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriisopropoxysilane, phenyltri-t-butoxy silane, dimethyldichlorosilane, dimethyldibromosilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldichlorosilane, diphenyldibromosilane, diphenyldimethoxysilane, diphenyldiethoxysilane, phenylmethyldichlorosilane, phenylmethyldibromosilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, triethoxyhydrosilane, tribromohydrosilane, trimethoxyhydrosilane, isopropoxyhydrosilane, tri-t-butoxyhydrosilane, vinyltrichlorosilane, vinyltribromosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltri-t-butoxysilane, trifluoropropyltrichlorosilane, trifluoropropyltribromosilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, trifluoropropyltriisopropoxysilane, trifluoropropyltri-t-butoxysilane, xcex3glycidoxypropylmethyldimethoxysilane, xcex3-glycidoxypropylmethyldiethoxysilane, xcex3-glycidoxypropyltrimethoxysilane, xcex3-glycidoxypropyltriethoxysilane, xcex3-glycidoxypropyltriisopropoxysilane, xcex3-glycidoxypropyltri-t-butoxysilane, xcex3-methacryloxypropylmethyldimethoxysilane, xcex3-methacryloxypropylmethyldiethoxysilane, xcex3-methacryloxypropyltrimethoxysilane, xcex3-methacryloxypropyltriisopropoxysilane, xcex3-methacryloxypropyltri-t-butoxysilane, xcex3-aminopropylmethyldimethoxysilane, xcex3-aminopropylmethyldiethoxysilane, xcex3-aminopropyltrimethoxysilane, xcex3-aminopropyltriethoxysilane, xcex3-aminopropyltriisopropoxysilane, xcex3-aminopropyltri-t-butoxysilane, xcex3-mercaptopropylmethyldimethoxysilane, xcex3-mercaptopropylmethyldiethoxysilane, xcex3-mercaptopropyltrimethoxysilane, xcex3-mercaptopropyltriethoxysilane, xcex3-mercaptopropyltriisopropoxysilane, xcex3-mercaptopropyltri-t-butoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and xcex2-(3,4-epoxycyclohexyl)ethyltriethoxysilane.
Along with the silane compound represented by the general formula (II) used for forming the inorganic hydrophilic matrix of the hydrophilic layer of this embodiment, a metallic compound that can be formed into a film by bonding to the resin on the sol-gel conversion, such as Ti, Zn, Sn, Zr and Al, may be used in combination.
Examples of the metallic compound used include Ti(OR5)4 (wherein R5 represents a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group or a hexyl group), TiCl4, Ti(CH3COCHCOCH3)2(OR5)2, Zn(OR5)2, Zn(CH3COCHCOCH3)2, Sn(OR5)4, Sn(CH3COCHCOCH3)4, Sn(OCOR5)4, SnCl4, Zr(OR5)4, Zr(CH3COCHCOCH3)4, Al(OR5)3 and Al(CH3COCHCOCH3)3.
In order to accelerate the hydrolysis reaction and the polycondensation reaction of the silane compound represented by the general formula (II) and the metallic compound used in combination, it is preferred to use an acidic catalyst or a basic catalyst in combination.
As the catalyst, an acid or a base itself or those dissolved in water or a solvent, such as an alcohol, (hereinafter referred to as an acidic catalyst or a basic catalyst, respectively) are used. The concentration herein is not particularly limited, and there is a tendency that the rate of the hydrolysis or the polycondensation is increased when the concentration is high. However, when a basic catalyst of a high concentration is used, there are cases where a precipitate is formed in a sol solution, and therefore it is preferred that the concentration of the basic catalyst is 1N or less (in terms of the concentration in an aqueous solution).
The species of the acidic catalyst and the basic catalyst is not particularly limited. Specific examples of the acidic catalyst include a hydrogen halogenide, such as hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, hydrogen sulfide, perchloric acid, hydrogen peroxide, carbonic acid, a carboxylic acid, such as formic acid and acetic acid, a substituted carboxylic acid, wherein R in the structural formula RCOOH is substituted by another element or a substituent, and a sulfonic acid, such as benzenesulfonic acid, and specific examples of the basic catalyst include an ammonical base, such as aqueous ammonia, and an amine, such as ethylamine and aniline.
The details of the sol-gel process are described in known literatures, such as S. Sakuhana, xe2x80x9cSol-Gel Hou no Kagaku (Science of Sol-Gel Process)xe2x80x9d (published by Agune Shofu-sha (1988)), and M. Hirashima, xe2x80x9cSaishin Sol-Gel Process niyoru Kinousei Hakumaku Sakusei Gijutu (Formation Technique of Functional Thin Film by Newest Sol-Gel Process)xe2x80x9d (published by Sougou Gijutu Center (1992)).
Compounds for various purposes, such as control of the extent of the hydrophilicity, improvement of the physical strength of the hydrophilic layer, improvement of the dispersibility of the compositions constituting the layer improvement of the coating property and improvement of the printing suitability, may be added to the hydrophilic layer of this embodiment in addition to the foregoing components. Examples of the compounds include a plasticizer, a pigment, a coloring matter, a surface active agent and hydrophilic particles.
The hydrophilic particles are not particularly limited, and preferred examples thereof include silica, alumina, titanium oxide, magnesium oxide, magnesium carbonate and calcium alginate. These may be used for enhancing the hydrophilicity or enforcing the film. In the hydrophilic layer of the organic or inorganic hydrophilic matrix of this embodiment, it is a preferred embodiment that metallic oxide particles, such as silica, alumina and titanium oxide, are contained.
Silica has a large number of hydroxyl groups on the surface, and the interior thereof is constituted by a siloxane bond (xe2x80x94Sixe2x80x94Oxe2x80x94Sixe2x80x94). Examples of the silica that can be preferably used in this embodiment include silica super-fine particles having a particle diameter of from 1 to 100 nm dispersed in water of a polar solvent, which is also referred to as a colloidal silica. Specific details thereof are described in T. Kagami and E. Hayashi, xe2x80x9cKoujundo Silica no Ouyou Gijutu (Application Technique of High Purity Silica)xe2x80x9d, (published by CMC Publications (1991)).
Examples of the alumina that can be preferably used include alumina hydrate (boehmite series) having a colloid size of from 5 to 200 nm having been dispersed in water with an anion (for example, a halogenide ion, such as a fluoride ion and a chloride ion, and a carboxylic anion, such as acetic acid ion) as a stabilizer.
Examples of the titanium oxide that can be preferably used include anatase type or rutile type titanium oxide having an average primary particle diameter of from 50 to 500 nm dispersed in water or a polar solvent by using, depending on necessity, a dispersing agent.
The average primary particle diameter of the hydrophilic particles that can be preferably used in this embodiment is from 1 to 5,000 nm, and more preferably from 10 to 1,000 nm.
In the hydrophilic layer of this embodiment, the hydrophilic particles may be used singly as one kind or may be used in combination of two or more kinds. The usage amount thereof is from 5 to 80% by weight, preferably from 10 to 70% by weight, and more preferably from 20 to 60% by weight, based on the total solid content of the hydrophilic layer.
The hydrophilic layer of the organic or inorganic hydrophilic matrix used in this embodiment is formed, for example, in such a manner that the components are dissolved or dispersed in a solvent, such as water or a polar solvent, e.g., methanol and ethanol, solely or as a mixed solvent thereof, and the resulting solution is then coated, dried and hardened on the heat-sensitive layer.
The coating amount thereof is, in terms of the weight after drying, suitably from 0.1 to 20 g/m2, preferably from 0.3 to 10 g/m2, and more preferably from 0.5 to 5 g/m2. If the coating amount of the hydrophilic layer after drying is less than 0.1 g/m2, undesirable results are obtained such as decrease of the maintaining property of wetting water and decrease of the film strength, and if it is higher, undesirable results are also obtained such as decrease in the sensitivity and difficulty in removal at the exposed part.
The thin film of a metal or a metallic compound having a hydrophilic surface used in the hydrophilic layer of this embodiment is not particularly limited as long as it has a hydrophilic surface, and examples thereof include a metal, such as aluminum, chromium, manganese, tin, tellurium, titanium, iron, cobalt, nickel, indium, bismuth, zirconium, zinc, lead, vanadium, silicon, copper and silver, and an alloy thereof, as well as a metallic oxide, a metallic carbide, a metallic nitride, a metallic boride, a metallic sulfide and a metallic halogenide corresponding to the respective metals. The surface of the thin film of the metals and the metallic compounds is practically in a highly oxidized state, which advantageously serves as the hydrophilicity. Therefore, a thin film of a metallic oxide, such as indium tin oxide, tungsten oxide, manganese oxide, silicon oxide, titanium oxide, aluminum oxide and zirconium oxide, is preferably used as the hydrophilic layer of this embodiment.
The thin film of a metal or a metallic compound having a hydrophilic surface used in the hydrophilic layer of this embodiment can be formed by a PVD process (physical vapor deposition process), such as a vacuum vapor deposition process, a sputtering process and an ion plating process, and a CVD process (chemical vapor deposition process). Examples of the heating method in the vacuum vapor deposition process include resistance heating, high frequency induction heating and electron beam heating.
It is also possible that oxygen or nitrogen is introduced as a reactive gas, and reactive vapor deposition is conducted by using addition of ozone and ion assistance.
In the case where the sputtering process is employed, a pure metal or the objective oxide can be used as a target material, and when a pure metal is used, oxygen is introduced as a reactive gas. Examples of the sputtering power source include a direct current power source, a pulse direct current power source and a high frequency power source.
Before forming the thin film, in order to improve adhesion to the heat-sensitive layer, a substrate degasification treatment by heating the substrate or a vacuum glow treatment on the ink receiving surface may be conducted. For example, in the vacuum glow treatment, a high frequency wave is applied to the substrate under a pressure of from 1 to 10 mtorr to form glow discharge, and the substrate is treated with the resulting plasma. It is also possible that the effect is enhanced by increasing the applied voltage or introducing a reactive gas, such as oxygen and nitrogen.
The thickness of the thin film of a metal or a metallic compound having a hydrophilic surface used in the hydrophilic layer of this embodiment is preferably from 10 to 3,000 nm, and more preferably from 20 to 1,500 nm. If the film is too thin, undesirable results, such as decrease in maintaining property of the hydrophilic component of the emulsion ink and decrease in the film strength, are obtained. If the film is too thick, undesirable results, such as decrease in the image recording sensitivity, are also obtained.
The heat-sensitive layer that can be used in this embodiment is such a layer that the surface thereof is chemically and/or physically changed by heat to decrease the adhesion to the hydrophilic layer as the upper layer, and that functions as an image portion receiving an oleophilic ink component upon printing. The heat-sensitive layer contains an organic polymer having a surface that has an oleophilic ink receiving property and a thermoplastic property (thermosoftening property) or a pyrolytic property.
The heat-sensitive layer used in this embodiment may be coated on the substrate, or in alternative, in the case where the substrate itself has such a surface that has an oleophilic ink receiving property and a thermoplastic property (thermosofteneing property) or a pyrolytic property (for example, a plastic film or a substrate having a plastic film laminated thereon), the substrate may have the function of the heat-sensitive layer. Details of the substrate will be described later.
The organic polymer used in the heat-sensitive layer of this embodiment has a function of forming an oleophilic film and also has a thermoplastic property (thermosofteneing property) or a pyrolytic property. Furthermore, it is preferred that the polymer is insoluble in a coating solvent for forming the hydrophilic layer as the upper layer, but in some cases, a polymer that is swollen with the coating solvent for the upper layer is preferred since the polymer is excellent in adhesion property to the upper layer. In the case where an organic polymer that is soluble in the coating solvent for the upper layer is used, it is preferred to conduct some measures, for example, hardening by adding a crosslinking agent in advance.
Examples of the organic polymer that can be used include polyester, polyurethane, polyurea, polyimide, polysiloxane, polycarbonate, a phenoxy resin, an epoxy resin, a phenol-formaldehyde resin, an alkylphenol-formaldehyde resin, polyvinyl acetate, an acrylic resin and a copolymer thereof, polyvinyl phenol, polyvinyl halogenated phenol, a methacrylic resin and a copolymer thereof, an acrylamide copolymer, a methacrylamide copolymer, polyvinyl formal, polyamide, polyvinyl butyral, polystyrene, a cellulose ester resin, polyvinyl chloride and polyvinylidene chloride.
Among these, a resin having a hydroxyl group, a carboxyl group, a sulfonamide group or a trialkoxysilyl group on the side chain is preferred since it is excellent in adhesion property to the substrate and the hydrophilic layer as the upper layer, and in some cases, it is easily hardened with a crosslinking agent. Furthermore, a polymer obtained by photo-curing an acrylonitrile copolymer, polyurethane, a copolymer having a sulfonamide group on the side chain or a copolymer having a hydroxyl group on the side chain with a diazo resin is preferable.
Examples of the usable resin also include a novolak resin and a resol resin formed by condensation of formaldehyde and a phenol compound, such as phenol, cresol (such as m-cresol, p-cresol and a mixture of m-cresol and p-cresol), a mixture of phenol and cresol (such as m-cresol, p-cresol and a mixture of m-cresol and p-cresol), phenol-modified xylene, tert-butylphenol, octylphenol, resorcinol, pyrogallol, catechol, chlorophenol (such as m-chlorophenol and p-chlorophenol), bromophenol (such as m-bromophenol and p-bromophenol), salicylic acid and phloroglucinol, and a condensed resin of the phenol compound and acetone.
Examples of the preferred resin further include a copolymer that generally has a molecular weight of from 10,000 to 200,000 having the following monomers (1) to (12) as a constitutional unit:
(1) an acrylamide, a methacrylamide, an acrylate, a methacrylate and a hydroxystyrene that have an aromatic hydroxyl group, for example, N-(4-hydroxyphenyl)acrylamide, N-(4-hydroxyphenyl)methacrylamide, o-, m- or p-hydroxystyrene, and o-, m- or p-hydroxyphenyl acrylate or methacrylate;
(2) an acrylate and a methacrylate that have an aliphatic hydroxyl group, for example, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate;
(3) a (substituted) acrylate, for example, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, cyclohexyl acrylate, octyl acrylate, phenyl acrylate, benzyl acrylate, 2-chloroethyl acrylate, 4-hydroxybutyl acrylate, glycidyl acrylate and N-dimethylaminoethyl acrylate;
(4) a (substituted) methacrylate, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, octyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-chloroethyl methacrylate, 4-hydroxybutyl methacrylate, glycidyl methacrylate and N-dimethylaminoethyl methacrylate;
(5) an acrylamide and a methacrylamide, for example, acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, N-hexylacrylamide, N-hexylmethacrylamide, N-cyclohexylacrylamide, N-cyclohexylmethacrylamide, N-hydroxyethylacrylamide, N-hydroxyethylmethacrylamide, N-phenylacrylamide, N-phenylmethacrylamide, N-benzylacrylamide, N-benzylmethacrylamide, N-nitrophenylacrylamide, N-nitrophenylmethacrylamide, N-ethyl-N-phenylacrylamide and N-ethyl-N-phenylmethacrylamide;
(6) a vinyl ether, for example, ethyl vinyl ether, 2-chloroethyl vinyl ether, hydroxyethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, octyl vinyl ether and phenyl vinyl ether;
(7) a vinyl ester, for example, vinyl acetate, vinyl chloroacetate, vinyl butyrate and vinyl benzoate;
(8) a styrene, for example, styrene, methylstyrene and chloromethylstyrene;
(9) a vinyl ketone, for example, methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone and phenyl vinyl ketone;
(10) an olefin, for example, ethylene, propylene, isobutylene, butadiene and isoprene;
(11) N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine, acrylonitrile and methacrylonitrile; and
(12) an acrylamide, for example, N-(o-aminosulfonylphenyl)acrylamide, N-(m-aminosulfonylphenyl)acrylamide, N-(p-aminosulfonylphenyl)acrylamide, N-(1-(3-aminosulfonyl)naphthyl)acrylamide and N-(2-aminosulfonylethyl)acrylamide, a methacrylamide, for example, N-(o-aminosulfonylphenyl)methacrylamide, N-(m-aminosulfonylphenyl)methacrylamide, N-(p-aminosulfonylphenyl)methacrylamide, N-(1-(3-aminosulfonyl)naphthyl)methacrylamide and N-(2-aminosulfonylethyl)methacrylamide, an unsaturated sulfonamide of an acrylate, for example, o-aminosulfonylphenyl acrylate, m-aminosulfonylphenyl acrylate, p-aminosulfonylphenyl acrylate and 1-(3-aminosulfonylphenylnaphthyl) acrylate, and an unsaturated sulfonamide of a methacrylate, for example, o-aminosulfonylphenyl methacrylate, m-aminosulfonylphenyl methacrylate, p-aminosulfonylphenyl methacrylate and 1-(3-aminosulfonylphenylnaphthyl) methacrylate.
Examples of the pyrolytic organic polymer used in this embodiment include nitrocellulose and a binder used for the so-called xe2x80x9cchemical amplification systemxe2x80x9d disclosed in J. Imaging Sci., p. 59-64, vol. 30(2) (1986) (Frechet, et al.), Polymers in Electronics (Symposium Series, p. 11, 242, T. Davidson, Ed., ACS Washington, D.C. (1984) (Ito and Willson) and Microelectronic Engineering, p. 3-10, vol. 13 (1991) (E. Reichmanis and L. F. Thompson), but the present invention is not limited thereto.
The polymer compound may be used singly or in a combination of two or more.
The organic polymer is dissolved in an appropriate solvent and then coated and dried on the substrate to provide the heat-sensitive layer on the substrate. The organic polymer may be solely dissolved in a solvent, but in general, the organic polymer is used along with a crosslinking agent, an adhesion assistant, a coloring agent, inorganic or organic fine particles, a coating surface improving agent and a plasticizer.
In the heat-sensitive layer, a pyrolytic compound for increasing the laser recording sensitivity, a photothermal conversion substance and a thermal coloring system or a thermal decoloring system for forming a print out image after exposure may be added.
Specific examples of the known crosslinking agent for crosslinking the organic polymer include a diazo resin, an aromatic diazo compound, a polyfunctional isocyanate compound, a polyfunctional epoxy compound, a polyfunctional amine compound, a polyol compound, a polyfunctional carboxyl compound, an aldehyde compound, a polyfunctional (meth)acrylic compound, a polyfunctional vinyl compound, a polyfunctional mercapto compound, a polyvalent metallic salt compound, a polyalkoxysilane compound, a polyalkoxytitanium compound, a polyalkoxyaluminum compound, a polymethylol compound and a polyalkoxymethyl compound, and a known reaction catalyst may be added to accelerate the reaction. The usage amount thereof is from 0 to 50% by weight, preferably from 3 to 40% by weight, and more preferably from 5 to 35% by weight, based on the total solid content of the coating liquid for the heat-sensitive layer.
As the adhesion assistant, the diazo resin is excellent in adhesion between the substrate and the hydrophilic layer, and also a silane coupling agent, an isocyanate compound and a titanium series coupling agent are useful.
As the coloring agent, ordinary dyes and pigments can be used, and particularly, examples thereof include Rhodamine 6G chloride, Rhodamine B chloride, Crystal Violet, Malachite Green oxalate, Oxazine 4 perchlorate, quinizarin, 2-(xcex1-naphthyl)-5-phenyloxazole and coumarin 4. Specific examples of the other dyes include trephenylmethane series, diphenylmethane series, oxazine series, xanthene series, iminonaphthoquinone series, azomethine series and anthraquinone series dyes, such as Oil Yellow #101, Oil Yellow #103, Oil Pink #312, Oil Green BG, Oil Blue BOS, Oil Blue #603, Oil Black BY, Oil Black BS, Oil Black T-505 (all produced by Orient Chemical Industries, Ltd.), Victoria Pure Blue, Crystal Violet (C.I. 42555), Methyl Violet (C.I. 42535), Ethyl Violet, Methylene Blue (C.I. 52015), Patent Pure Blue (produced by Sumitomo Mikuni Chemical Co., Ltd.), Brilliant Blue, Methyl Green, Erythricine B, basic fuchsin, m-Cresol Purple, auramine, 4-p-diethylaminophenyliminaphthoquisine, and cyano-p-diethylaminophenylacetanilide, and the dyes disclosed in JP-A-62-293247 and Japanese Patent Application No. 7-335145.
When the dye is added to the heat-sensitive layer, it is generally present in an amount of about from 0.02 to 10% by weight, and preferably about from 0.1 to 5% by weight, based on the total solid content of the heat-sensitive layer.
A fluorine series surface active agent and a silicone series surface active agent, which are well known as a coating surface improving agent, can be used. Specifically, a surface active agent having a perfluoroalkyl group or a dimethylsiloxane group is useful for setting the coating surface.
Examples of the inorganic or organic fine powder include colloidal silica and colloidal aluminum each having a diameter of from 10 to 100 nm, and inert particles having a diameter larger than the colloid, such as silica particles, silica particles having a hydrophobic surface, alumina particles, titanium dioxide particles, other heavy metal particles, clay and talc. When the inorganic or organic fine powder is added to the heat-sensitive layer, the adhesion property to the hydrophilic layer as the upper layer is improved to enhance the printing durability upon printing. The addition amount of the fine powder in the heat-sensitive layer is preferably 80% by weight or less, and more preferably 40% by weight or less, based on the total amount.
In the heat-sensitive layer of this embodiment, a pyrolytic compound is added for improving the laser recording sensitivity. As such a compound, a known compound that generates a gas by decomposition upon heating can be added. In this case, the laser recording sensitivity can be improved by abrupt increase in volume on the surface of the heat-sensitive layer. Examples of the additive include dinitropentamethylene tetramine, N,Nxe2x80x2-dimethyl-N,Nxe2x80x2-dinitrosoterephthalamide, p-toluenesulfonylhydrazide, 4,4-oxybis(benzenesulfonylhydrazide) and diamidebenzene.
As the pyrolytic compound improving the laser recording sensitivity, a compound known as a thermal acid generating agent that generates an acidic compound through decomposition by heating, such as various kinds of an iodonium salt, a sulfonium salt, sulfonium tosylate, oxime sulfonate, dicarbodiimide sulfonate and triazine, can be used. When these compounds are used with a chemical sensitizing binder, the decomposition temperature of the chemical sensitizing binder that is the constitutional substance of the heat-sensitive layer, and as a result, the laser recording sensitivity can be increased.
The addition amount thereof is preferably from 1 to 20% by weight, and more preferably from 5 to 10% by weight, based on the total amount of the heat-sensitive layer.
Furthermore, in order to increase the laser recording sensitivity, the dye or pigment having infrared absorption property exemplified as the photothermal conversion agent may be added to the heat-sensitive layer of this embodiment. In the case where it is added to the heat-sensitive layer, an oleophilic dye or pigment may be used. The addition amount thereof is preferably from 1 to 20% by weight, and more preferably from 5 to 15% by weight, based on the total amount of the heat-sensitive layer.
In the heat-sensitive layer of this embodiment, a plasticizer may be added to impart flexibility to the coated film. Examples thereof include polyethylene glycol, tributyl citrate, diethyl phthalate, dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, tricresyl phosphate, tributyl phosphate, trioctyl phosphate, tetrahydrofurfuryl oleate and an oligomer or a polymer of acrylic acid or methacrylic acid.
In order to clearly distinguish the image portion and the non-image portion upon exposure, a compound of a coloring system or a decoloring system is preferably added to the heat-sensitive layer of this embodiment. For example, a leuco dye (such as Leuco Malachite Green, Leuco Crystal Violet and a lactonized compound of Crystal Violet) and a PH discoloration dye (for example, a dye, such as Ethyl Violet and Victoria Pure Blue BOH) are used along with a thermal acid generating agent, such as a diazo compound and a diphenyliodonium salt. The combination of an acid coloring dye and an acidic binder disclosed in EP 897134 is also effective. In this case, the bond of the association state forming the dye is broken by heat, and a lactonized compound is formed to change from a colored substance to a colorless substance.
The addition amount of the coloring system is preferably 10% by weight or less, and preferably 5% by weight or less, based on the total amount of the heat-sensitive layer.
Examples of the solvent used for coating to form the heat-sensitive layer include an alcohol (such as methanol, ethanol, propyl alcohol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether and ethylene glycol monoethyl ether), an ether (such as tetrahydrofuran, ethylene glycol dimethyl ether, propylene glycol dimethyl ether and tetrahydropyran), a ketone (such as acetone, methyl ethyl ketone and acetylacetone), an ester (such as methyl acetate and ethylene glycol monomethyl monoacetate), an amide (such as formamide, N-methylformamide, pyrrolidone and N-methylpyrrolidone), xcex3-butyrolactone, methyl lactate and ethyl lactate.
The solvents are used singly or as a mixture. Upon preparing a coating liquid, the concentration of the constitutional components of the heat-sensitive layer (all the solid contents including the additives) in the solvent is preferably from 1 to 50% by weight. In addition to the coating from the organic solvent, the coating film may be formed with an aqueous emulsion. In this case, the concentration is preferably from 5 to 50% by weight.
The thickness of the heat-sensitive layer in this embodiment after coating and drying is not particularly limited, and may be from 0.05 to 5 g/m2, and preferably from 0.05 to 3 g/m2. In the case where the heat-sensitive layer is formed on a metallic plate, it is desirably 0.5 g/m2 or more, and more preferably from 0.5 to 3 g/m2 since it functions as a thermal insulating layer.
If the heat-sensitive layer is too thin, the generated heat is scattered toward the metallic plate to decrease the sensitivity. In the case of the hydrophilic metallic plate, furthermore, since the heat-sensitive layer is required to have wearing resistance as an ink receiving layer, the printing durability cannot be maintained. In the case where an oleophilic plastic film is used as the substrate, since scattering of heat is low, the coating amount can be smaller than the case of the metallic film and is preferably 0.05 g/m2 or more, and the coating amount after drying is preferably about from 0.05 to 3 g/m2.
As the substrate for the lithographic printing plate original that can be applied to the method of this embodiment, a plate having properties, such as strength and durability, that are required for a lithographic printing plate and having dimensional stability can be used through appropriate selection, and examples thereof include paper, paper having oleophilic plastics (such as polyethylene, polypropylene and polystyrene) laminated thereon, a metallic plate (such as aluminum, zinc, copper, nickel and stainless steel), a plastic film (such as cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose lactate, cellulose acetate lactate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate and polyvinyl acetal) and the plastic film having a oleophilic organic polymer resin coated thereon.
Preferred examples of the substrate include a polyethylene terephthalate film, a polycarbonate film, an aluminum or steel plate and an aluminum or steel plate having an oleophilic plastic film laminated thereon.
An aluminum plate that is preferably used in this embodiment is a pure aluminum plate, an alloy plate containing aluminum as the main component and a slight amount of other elements, and those having an ink receiving polymer compound coated thereon or having an ink receiving plastic film laminated thereon.
Examples of the other elements contained in the aluminum alloy include silicon, iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel and titanium. The content of the other elements in the alloy is 10% by weight at most. An aluminum plate formed with a conventionally known material can be used as the aluminum plate applied to this embodiment.
It is preferred that the surface of the aluminum plate is subjected to roughening before use. In the case where the ink receiving layer containing an organic polymer is coated on the substrate, the adhesion between the substrate and the ink receiving layer can be ensured by conducting the roughening treatment.
The roughening treatment will be described in order. Before conducting the roughening treatment, a degreasing treatment with a surface active agent, an organic solvent or an alkaline aqueous solution is conducted to remove a rolling oil on the surface of the aluminum substrate.
The roughening treatment of the surface of the aluminum plate is conducted by various methods, and for example, a method of mechanically roughening, a method of electrochemically dissolving the surface to be roughened and a method of chemically and selectively dissolving the surface are generally employed. As the method of mechanically roughening, a known method, such as a ball grinding method, a brush grinding method, a blast grinding method and a buff grinding method, can be used. As the chemical roughening method, a method of immersing in a saturated aqueous solution of an aluminum salt of a mineral acid as disclosed in JP-A-54-31187 is suitable. As the electrochemical roughening method, a method where the electrochemical roughening is conducted with an alternating current or a direct current in an electrolyte containing an acid, such as hydrochloric acid and nitric acid. An electrolytic roughening method using a mixed acid as disclosed in JP-A-54-63902 can also be utilized.
The roughening by the foregoing methods is preferably conducted to such an extent that the center line surface roughness (Ha) of the surface of the aluminum plate is in the range of from 0.3 to 1.0 xcexcm.
The aluminum plate having the surface having been roughened is subjected, depending on necessity, to an alkali etching treatment using an aqueous solution of potassium hydroxide or sodium hydroxide, followed by subjecting to a neutralizing treatment, and is further subjected to an anodic oxidation treatment to increase the wear resistance depending on necessity.
As the electrolyte used in the anodic oxidation treatment of the aluminum plate, various electrolytes that form a porous oxide film can be used, and in general, sulfuric acid, hydrochloric acid, oxalic acid, chromic acid and a mixed acid thereof are used. The concentration of the electrolyte is appropriately selected depending on the species of the electrolyte.
The treatment conditions for the anodic oxidation cannot be determined without condition since they vary depending on the species of the electrolyte used, and in general, appropriate conditions include a concentration of the electrolyte of from 1 to 80% by weight, a liquid temperature of from 5 to 70xc2x0 C., an electric current density of from 5 to 60 A/dm2, a voltage of from 1 to 100 V and an electrolysis time of from 10 seconds to 5 minutes.
The amount of the oxide film thus formed is preferably from 1.0 to 5.0 g/m2, and particularly preferably from 1.5 to 4.0 g/m2.
In the case where a non-electroconductive substrate, such as polyester, is used as the substrate of this embodiment, it is preferred that an antistatic layer is formed on the side of the heat-sensitive layer of the substrate, the opposite side to the heat-sensitive layer thereof, or both sides thereof. As the antistatic layer, a polymer layer having metallic oxide fine particles or a matting agent dispersed therein can be used.
Examples of the material for the metallic oxide fine particles include TiO2, ZnO, SnO2, Al2O3, In2O3, MgO, BaO, MoO3, V2O5, a complex oxide thereof and these metallic oxide further having a hetero atom. These metallic oxide may be used singly or in combination of two or more thereof. As the metallic oxide, ZnO, SnO2, Al2O3, In2O3 and MgO are preferred, ZnO, SnO2, Al2O3 and In2O3 are more preferred, and SnO2 is particularly preferred.
Examples of the metallic oxide containing a small amount of a hetero atom include ZnO doped with Al or In, SnO2 doped with Sb, Nb or a halogen element and In2O3 doped with Sn, in an amount of from 30 to 10% by mole.
It is preferred that the metallic oxide fine particles are contained in the antistatic layer in an amount of from 10 to 90% by weight. The average particle diameter of the metallic oxide fine particles is preferably from 0.001 to 0.5 xcexcm. The average particle diameter used herein is a value considering not only the primary particle diameter but also the particle diameter of particles having higher order structures of the metallic oxide fine particles.
Examples of the matting agent used in the antistatic layer include inorganic or organic particles having an average particle diameter of from 0.5 to 20 xcexcm, and more preferably from 1.0 to 15 xcexcm. Examples of the inorganic particles include a metallic oxide, such as silicon oxide, aluminum oxide, titanium oxide and zinc oxide, and a metallic salt such as calcium carbonate, barium sulfate, barium titanate and strontium titanate. Examples of the organic particles include crosslinked particles of polymethyl methacrylate, polystyrene, polyolefin and a copolymer thereof.
The matting agent is preferably contained in the antistatic layer in an amount of from 1 to 30% by weight.
Examples of the polymer that can be used in the antistatic layer include protein, such as gelatin and casein, a cellulose compound, such as carboxymethyl cellulose, hydroxyethyl cellulose, acetyl cellulose, diacetyl cellulose and triacetyl cellulose, a saccharide, such as dextran, agar, sodium alginate and a starch derivative, and a synthetic polymer such as polyvinyl alcohol, polyvinyl acetate, polyacrylate, polymethacrylate, polystyrene, polyacrylamide, polyvinylpyrrolidone, polyester, polyvinyl chloride, polyacrylic acid and polymethacrylic acid.
The polymer is preferably contained in the antistatic layer in an amount of from 10 to 90% by weight.
The substrate used in this embodiment preferably has a maximum roughness depth (Rt) of the back surface of the substrate of 1.2 xcexcm or more for the prevention of blocking, and preferably has a dynamic friction coefficient (xcexck) of 2.6 or less, which is measured by contacting the back surface of the substrate (i.e., the back surface of the lithographic printing plate original of this embodiment) and the surface of the lithographic printing plate original of this embodiment.
The thickness of the substrate used in this embodiment is generally about from 0.05 to 0.6 mm, preferably from 0.1 to 0.4 mm, and particularly preferably from 0.15 to 0.3 mm.
The lithographic printing plate original that can be subjected to the printing process of this embodiment has the foregoing constitution. The image recording process and the printing process of the lithographic printing plate original will be described below.
The image recording of the lithographic printing plate original of this embodiment includes a step of imagewise heating by heating or exposure to laser light. For example, the step is effected by imagewise heat-sensitive recording directly by a thermal recording head, imagewise scanning exposure by a solid laser or a semiconductor laser emitting an infrared ray having a wavelength of from 700 to 1,200 nm, or photothermal conversion type exposure, such as planar exposure by a light source, for example, with high illuminance flash light, such as that from a xenon discharge lamp, or an infrared ray lamp.
In this embodiment, laser light is particularly preferably used. The energy of the laser light used for image recording is adsorbed and converted to heat energy by the photothermal conversion substance contained in the heat-sensitive lithographic printing plate original of this embodiment, and the heat-sensitive lithographic printing plate original of this embodiment is imagewise heated by the heat thus generated to enable release of the heated part of the hydrophilic layer, whereby the image recording is effected.
The laser used for recording in this embodiment is not particularly limited as long as it can provide an exposure amount that is necessary for generating heat sufficient to effect recording on the heat-sensitive lithographic printing plate original of this embodiment. Usable examples thereof include a gas laser, such as an Ar laser and a carbon dioxide gas laser, a solid laser, such as a YAG laser, and a semiconductor laser, and in general, a laser of a class having an output power of 50 mW or higher is necessary. A semiconductor laser and a solid laser excited by a semiconductor (such as a YAG laser) are preferably used from the practical standpoint of maintainability and cost. The recording wavelength of the laser is in a wavelength region of an infrared ray, and an oscillation wavelength of from 700 to 1,200 nm is often used. It is also possible to conduct the exposure by using an imaging apparatus disclosed in JP-A-6-186750.
The heat-sensitive lithographic printing plate original of this embodiment can be subjected to printing in such a manner that the original plate having been subjected to image recording can be mounted on a printing machine to be used for printing without subjecting any further treatment, i.e., without a development treatment.
When the lithographic printing plate having been subjected to image recording is mounted on a printing machine, and printing is started by using an emulsion ink, the overcoat layer is removed with the hydrophilic component of the emulsion ink, and simultaneously, the hydrophilic layer at the exposed part, which is decreased in adhesion property to the heat-sensitive layer, is also removed. Thus, the development is effected, whereby the hydrophilic layer remaining as a non-exposed part becomes an ink repelling region (non-image portion), and the hydrophilic component of the emulsion ink is attached to the hydrophilic layer. The part where the hydrophilic layer is released to expose the oleophilic heat-sensitive layer forms a region of high affinity to the ink (image portion), and the oleophilic ink component in the emulsion ink is attached to the exposed heat-sensitive layer, so as to start printing.